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Subject[PATCH 1/7] Revert: "softirq: Add support for triggering softirq work on softirqs"
This commit was incomplete in that code to remove items from the per-cpu
lists was missing and never acquired a user in the 5 years it has been
in the tree. We're going to implement what it seems to try to archive
in a simpler way, and this code is in the way of doing so.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
include/linux/interrupt.h | 22 --------
kernel/softirq.c | 131 ---------------------------------------------
2 files changed, 153 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 5e865b5..8c0d4ba 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -11,8 +11,6 @@
#include <linux/irqnr.h>
#include <linux/hardirq.h>
#include <linux/irqflags.h>
-#include <linux/smp.h>
-#include <linux/percpu.h>
#include <linux/hrtimer.h>
#include <linux/kref.h>
#include <linux/workqueue.h>
@@ -381,15 +379,6 @@ extern void __raise_softirq_irqoff(unsigned int nr);
extern void raise_softirq_irqoff(unsigned int nr);
extern void raise_softirq(unsigned int nr);

-/* This is the worklist that queues up per-cpu softirq work.
- *
- * send_remote_sendirq() adds work to these lists, and
- * the softirq handler itself dequeues from them. The queues
- * are protected by disabling local cpu interrupts and they must
- * only be accessed by the local cpu that they are for.
- */
-DECLARE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
-
DECLARE_PER_CPU(struct task_struct *, ksoftirqd);

static inline struct task_struct *this_cpu_ksoftirqd(void)
@@ -397,17 +386,6 @@ static inline struct task_struct *this_cpu_ksoftirqd(void)
return this_cpu_read(ksoftirqd);
}

-/* Try to send a softirq to a remote cpu. If this cannot be done, the
- * work will be queued to the local cpu.
- */
-extern void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq);
-
-/* Like send_remote_softirq(), but the caller must disable local cpu interrupts
- * and compute the current cpu, passed in as 'this_cpu'.
- */
-extern void __send_remote_softirq(struct call_single_data *cp, int cpu,
- int this_cpu, int softirq);
-
/* Tasklets --- multithreaded analogue of BHs.

Main feature differing them of generic softirqs: tasklet
diff --git a/kernel/softirq.c b/kernel/softirq.c
index d7d498d..c587b7f 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -6,8 +6,6 @@
* Distribute under GPLv2.
*
* Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
- *
- * Remote softirq infrastructure is by Jens Axboe.
*/

#include <linux/export.h>
@@ -618,146 +616,17 @@ void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
}
EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);

-/*
- * Remote softirq bits
- */
-
-DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
-EXPORT_PER_CPU_SYMBOL(softirq_work_list);
-
-static void __local_trigger(struct call_single_data *cp, int softirq)
-{
- struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
-
- list_add_tail(&cp->list, head);
-
- /* Trigger the softirq only if the list was previously empty. */
- if (head->next == &cp->list)
- raise_softirq_irqoff(softirq);
-}
-
-#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
-static void remote_softirq_receive(void *data)
-{
- struct call_single_data *cp = data;
- unsigned long flags;
- int softirq;
-
- softirq = *(int *)cp->info;
- local_irq_save(flags);
- __local_trigger(cp, softirq);
- local_irq_restore(flags);
-}
-
-static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
-{
- if (cpu_online(cpu)) {
- cp->func = remote_softirq_receive;
- cp->info = &softirq;
- cp->flags = 0;
-
- __smp_call_function_single(cpu, cp, 0);
- return 0;
- }
- return 1;
-}
-#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
-static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
-{
- return 1;
-}
-#endif
-
-/**
- * __send_remote_softirq - try to schedule softirq work on a remote cpu
- * @cp: private SMP call function data area
- * @cpu: the remote cpu
- * @this_cpu: the currently executing cpu
- * @softirq: the softirq for the work
- *
- * Attempt to schedule softirq work on a remote cpu. If this cannot be
- * done, the work is instead queued up on the local cpu.
- *
- * Interrupts must be disabled.
- */
-void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
-{
- if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
- __local_trigger(cp, softirq);
-}
-EXPORT_SYMBOL(__send_remote_softirq);
-
-/**
- * send_remote_softirq - try to schedule softirq work on a remote cpu
- * @cp: private SMP call function data area
- * @cpu: the remote cpu
- * @softirq: the softirq for the work
- *
- * Like __send_remote_softirq except that disabling interrupts and
- * computing the current cpu is done for the caller.
- */
-void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
-{
- unsigned long flags;
- int this_cpu;
-
- local_irq_save(flags);
- this_cpu = smp_processor_id();
- __send_remote_softirq(cp, cpu, this_cpu, softirq);
- local_irq_restore(flags);
-}
-EXPORT_SYMBOL(send_remote_softirq);
-
-static int remote_softirq_cpu_notify(struct notifier_block *self,
- unsigned long action, void *hcpu)
-{
- /*
- * If a CPU goes away, splice its entries to the current CPU
- * and trigger a run of the softirq
- */
- if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
- int cpu = (unsigned long) hcpu;
- int i;
-
- local_irq_disable();
- for (i = 0; i < NR_SOFTIRQS; i++) {
- struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
- struct list_head *local_head;
-
- if (list_empty(head))
- continue;
-
- local_head = &__get_cpu_var(softirq_work_list[i]);
- list_splice_init(head, local_head);
- raise_softirq_irqoff(i);
- }
- local_irq_enable();
- }
-
- return NOTIFY_OK;
-}
-
-static struct notifier_block remote_softirq_cpu_notifier = {
- .notifier_call = remote_softirq_cpu_notify,
-};
-
void __init softirq_init(void)
{
int cpu;

for_each_possible_cpu(cpu) {
- int i;
-
per_cpu(tasklet_vec, cpu).tail =
&per_cpu(tasklet_vec, cpu).head;
per_cpu(tasklet_hi_vec, cpu).tail =
&per_cpu(tasklet_hi_vec, cpu).head;
- for (i = 0; i < NR_SOFTIRQS; i++)
- INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
}

- register_hotcpu_notifier(&remote_softirq_cpu_notifier);
-
open_softirq(TASKLET_SOFTIRQ, tasklet_action);
open_softirq(HI_SOFTIRQ, tasklet_hi_action);
}
--
1.7.10.4



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